Crimping of polyvinyl alcohol yarns by means of alkaline solutions



3,167,383 CRIB/{PING OF POLYVENYL ALCtH-EQL YARNS BY MEANS OF ALKALINE EQQLUTEUNS Jean (Ilaude Chezaud, Sat-liarnbcrt liie Barbe, and Henri Laehaussee, Lyon, France, assignors to Societe mediaceta, Paris, France, a French body corporate No Drawing. Filed st, 19, 3960, Ser. No. 63,483 Claims priority, appiication France Oct. 26, 1959 6 Qlaims. (Cl. 55-41155) This invention relates to the production of crimped yarns.

There are many methods of imparting to thermoplastic yarns a certain increase in volume and thus a more pleasant handle, so that their use is more desirable in many clothing applications. Some of these involve imparting a crimp to the yarns.

One of these methods consists in imparting a high degree of twist to the yarns, which twist is set by a heat treatment and thereafter removed by untwisting; all these operations can be carried out continuously using the socalled false-twisting technique.

In another method; use is made of a device having a sharp edge over which the heated yarns are passed, in an acute-angled path, of which the apex is situated on the edge.

It is also known to pack yarns under pressure in a vessel through which an agent is passed to set the deformations thus produced in the yarns.

It has furthermore been proposed to impart an appreciable increase in volume, as also a relatively dry handle, U

to yarns of various natures by subjecting them to the ac tion of a current of compressed air to which -a whirling movement is imparted, whereby small loops are formed in the individual filaments.

Finally, it is known to treat yarns based on polyamides with hydroxy compounds which are not solvents for the polymer and to subject them immediately to a heat treatment.

All these methods are mechanical or physical methods. Chemical crimping methods have not hitherto found any important practical applications.

According to the invention a crimped yarn is made by subjecting a yarn of an un-acetalised polyvinyl alcohol, to the action of an alkaline solution, preferably an aqueous alkali metal hydroxide solution until a crimp has developed in the yarn.

Preferably, the said yarns are thereafter acetalised in a manner known per se. A still better product is obtained if the said yarns, having been acetalised, are finally subjected to the action of an organic diisocyanate, preferably an aromatic diisocyanate. Soft high-bulk yarns are thereby obtained, whose crimp is stable and which are insoluble in boiling water.

The invention includes also the yarns thus obtained, and textile articles containing them.

In a preferred embodiment of the invention, the alkaline treatment is carried out in two stages by means of solutions of differing, preferably increasing, alkalinity, e.g.,

' alkali metal hydroxide solutions, such as caustic soda solutions, of different concentrations. The preferred concentrations are up to 20%, e.g., 10-20%, in the case of the first bath and between 35% and saturation, especially about 40%, in the case of the second bath when the operation is carried out at ambient temperature, say 25 C. The concentrations and the duration of the treatment can be varied in accordance with the temperature at which the treatment is carried out.

The acetalisation of the yarn is preferably effected with formaldehyde by a method known per se, in which the yarnis immersed in a bath containing sulphuric acid and sodium sulphate in addition to formaldehyde.

The treatment with a diisocyanate results in the setting United States Patent 0 3,167,383 Patented Jan. 26, 1965 "ice by cross-linking of the crimp imparted to the yarn; the diisccyanate is preferably used in solution in an organic solvent.

The following examples illustrate the invention without limiting its scope.

Example I The starting material is a continuous yarn based on non-acetalised polyvinyl alcohol and having a count of 1,200 denier/200 filaments. It is immersed successively in a 20% caustic soda solution for 3 hours, and a 40% caustic soda solution for 1 hour 10 minutes, both at ambient temperature. It is then rinsed three times, first with water at 50 C., then with 5% aqueous acetic acid, and finally with cold water. The yarn obtained has a high degree of crimp.

Example II The process of Example I is repeated, with the addition that the yarn obtained is treated with formaldehyde in order to render it insensitive to boiling water. This treatment is effected by immersing the yarn for 30 minutes at 60 C. in a bath having the following composition:

G. 30% formaldehyde 50 H (66 Be.) Na SO hydrate 150 Water 1000 The yarn is then rinsed in cold water and thoroughly dried. The product has a softer handle and a better highbulk effect.

Its crimp can be set by the following treatment with a diisocyanate. The yarn is immersed for 3 minutes at room temperature in an 0.5% solution of the product known under the tradename Desmodur R in methylene chloride, freed from liquid, and dried for 30 seconds at 150 C.

The yarn thus treated has a stabilised crimp and is insoluble in boiling water.

We claim:

1. Process for the production of a crimped yarn, which comprises immersing a yarn of polyvinyl alcohol in at least two solutions of increasing alkalinity until a crimp has developed in the yarn.

2. Process for the production of a crimped yarn, which comprises immersing a yarn of polyvinyl alcohol in at least two alkali metal hydroxide solutions of increasing alkalinity at a temperature of 15-25 C., the concentration of the first solution being 10-20% and that of the final solution being between 35% andsaturation.

3. Process for the production of a crimped yarn, which comprises immersing a yarn of polyvinyl alcohol successively in two aqueous sodium hydroxide solutions at a temperature of 15 25 C., the concentration of the first solution being essentially 20% and that of the second between 35% and saturation.

4. Process according to claim 2, which comprises also acetalising the crimped yarn obtained.

5. Process according to claim 2, which comprises also setting the crimp in the yarn by a treatment with an organic diisocyanate.

6. Process according to claim 5, which comprises also setting the crimp in the yarn by a treatment with an aromatic diisocyanate.

References tlited in the file of this patent UNITED STATES PATENTS 2,369,395 Heymann Feb. 13, 1945 2,413,789 Scheiderbauer Jan. 7, 1947 2,636,804 McClellan et a1. Apr. 28, 1953 2,749,208 Cline June 5, 1956 2,878,548 Lohr et al. Mar. 24, 1959 

1. PROCESS FOR THE PRODUCTION OF A CRIMPED YARN, WHICH COMPRISES IMMERSING A YARN OF POLYVINYL ALCOHOL IN AT LEAST TWO SOLUTIONS OF INCREASING ALKALINITY UNTIL A CRIMP HAS DEVELOPED IN THE YARN.
 3. PROCESS FOR THE PRODUCTION OF A CRIMPED YARN, WHICH COMPRISES IMMERSING A YARN OF POLYVINYL ALCOHOL SUCCESSIVELY IN TWO AQUEOUS SODIUM HYDROXIDE SOLUTIONS AT A TEMPERATURE OF 15*-25*C., THE CONCENTRATION OF THE FIRST SOLUTION BEING ESSENTIALLY 20% AND THAT OF THE SECOND BETWEEN 35% AND SATURATION. 